Lens Tracing Lite

The free version. UTC Lens Tracing Lite is the free edition of UTC Lens Tracing. It traces the light of every pixel through a real lens, exactly as the full version does, with four lenses to try. Editing lenses, the rest of the kit and final renders are in the full version: the table below says what is where.

How this page goes

You don't dial in a blur: you mount a lens and set the camera, and the lens's own glass shapes the bokeh, the dark corners and the distortion, as on set.

1. Your first shot: place the camera, check its lens, focus.
2. The four lenses: what each one brings, and how to look inside it.
3. The camera: sensor, exposure, and the switch for each lens effect.
4. Where it renders: what the Lite traces, and what it leaves to the full version.
5. Lite and full version, and moving to the full version.

The full tutorial goes further on every step. Where it mentions a row the Lite does not have, that row is in the full version.

Your first shot

The lenses and the Demo level are in Plugins > UTC Lens Tracing Lite Content (in the Content Browser, Settings > Show Plugin Content).

1. Place a Lens Tracing Cine Camera Actor (Quick Add, type Lens Tracing). It is a Cine Camera Actor: Sequencer and Blueprints use it as one.

   

2. Check the lens. A new camera comes with Standard_50mm, a 50 mm f/1.4, mounted: it is in Lens Tracing > Lens > Lens Data, in its Details. To mount another lens, pick it in that slot.

   

3. Look through it. Only views through a lens tracing camera are traced: your other cameras and viewports render as before.

4. Focus. Manual Focus Distance and its eyedropper are in Lens Tracing > Focus. A new camera is focused at 1 km.

What you are looking at is the 50 mm's own rendering, not a generic blur:

• The background melts into its bokeh: round in the middle, cat's eyes towards the corners.
• The corners darken a little, as on a fast lens wide open.
• Straight lines bow out slightly near the edges: the lens's own barrel distortion.
• The framing tightens a little as you focus closer: the lens breathes.

To compare with Unreal's ideal lens, set Active Lens to 1: no lens sits in that slot, so the camera renders as a plain Cine Camera. Set it back to 0 to mount the lens again.

The four lenses

Each one is a real optical design from an expired patent, with the designer's curvatures, spacings and glass. You pick one for its angle of view and its character. All four cover full frame.

Lens	Design	Widest stop	What you will see
Wide_28mm	Retrofocus, Olympus patent, 1975	f/2.8	Moderate barrel, darker corners wide open
Standard_50mm	Double Gauss, Nikon patent, 1981	f/1.4	The everyday fast fifty: gentle barrel, cat's eyes towards the corners wide open
Vintage_Fast_50mm	Ludwig Bertele's fast 50 for Zeiss Ikon, 1932	f/1.5	Pincushion, strong darkening towards the corners, stretched bokeh at the edges
Tele_180mm	Telephoto, Nikon patent, 1979	f/2.8	Slight pincushion, even corners, flattened perspective

The lens sets the focal length. Current Focal Length, in Current Camera Settings, greys out: it shows the framing focal length, breathing included.

Carry several. Add more slots to Lens Data; Active Lens says which one is mounted, counting from 0. It keys in Sequencer: a lens change on the frame, like a cut.

Look inside a lens. Double-click a lens in the Content Browser. Its window draws the glass to scale with the rays through it, the iris, the entrance pupil and the sensor, and lists its numbers: focal length, widest stop, image circle, distortion.

• Rays, Off-axis field and f/ change what the drawing shows: more rays, a second bundle from the edge of the field, a smaller iris. Ray tracing (dashed) adds the rays traced through the real glass surfaces next to the simplified ones the renderer uses.
• Drag to pan, wheel to zoom, double-click to fit.
• Move the mouse over a row of Surfaces in the Details: its surface lights up on the drawing.
• The lens is read-only in the Lite: Max Rays Per Pixel is the one row you can change, for a smoother bokeh at a higher cost. To modify a lens or build your own, the Lens Editor is in the full version.

The camera

The camera's Lens Tracing section, from top to bottom:

Focus works as on any Cine Camera, with one difference: distances are measured from the lens's entrance pupil, where the camera actor sits, not from the sensor mark.

Exposure. The camera has its own Shutter Speed and ISO next to Current Aperture. With Metering Mode on Manual they set the brightness, as on your camera; with an automatic mode Unreal sets it, and the aperture is free for its look. Current Aperture stops at the lens's widest stop.

Sensor. Unreal starts on a Super 35 sensor, and these lenses are full-frame designs, so they frame 1.5 times tighter on it. In Filmback, pick 16:9 DSLR for full frame, or tick Recommended Sensor: the camera takes the largest format the mounted lens covers.

Bokeh comes from the glass: round in the middle of the frame, cat's eyes towards the corners. The iris is round at every stop in the Lite; the iris blades, with their polygons as you stop down, are in the full version.

Lens Effects has one switch per optical trait, per camera, like a lens profile you turn on or off. All are ticked on a new camera. An unticked effect is never rendered, not corrected afterwards.

Switch	Unticked, you get
Focus Breathing	A framing that ignores focus, like a cine lens corrected for breathing
Distortion	Straight lines, as after a lens profile correction
Mechanical Vignetting	No cat's eyes and no glass-edge darkening: only the iris limits the light
Natural Vignetting	Even brightness out to the corners
Field Curvature	One flat plane of focus

Where it renders

The Lite traces:

• the editor's viewports looking through the camera,
• Play in Editor,
• High Resolution Screenshot through the camera.

Movie Render Queue and packaged games render the camera as a plain Cine Camera, with Unreal's own depth of field, and the Output Log says so once. They trace through the lens with the full version.

On the lens tracing camera, Unreal's depth of field and motion blur are off: the lens makes its own depth of field.

Tracing costs more GPU time than Unreal's depth of field, and more where the image is very blurred. While you work, type r.LensTracer.SampleDensity 0.5 in the console for a faster viewport, and 1 for your final screenshots.

Lite and full version

	Lite	Full version
The traced lens: bokeh, cat's eyes, distortion, vignetting, field curvature, breathing	Yes	Yes
Lenses	4 primes	10 primes and 2 zooms
Lens Effects switches, Recommended Sensor	Yes	Yes
Looking inside a lens	Drawing and numbers, read-only	The Lens Editor: change a lens, build one from scratch, import a real one from Optical Bench, make a zoom, with a test scene through the lens as you work
Iris	Round	Blades: count and rotation, polygonal bokeh as you stop down
Sensor	Format	Format, sensor noise from ISO, shutter and light, Auto ISO
Renders	Viewports, Play in Editor, High Resolution Screenshot	The same, Movie Render Queue and packaged games
Colour fringes, the lens's own motion blur	No	Experimental, by console command

UTC Lens Tracing on Fab

Moving to the full version

1. Disable or uninstall the Lite first: the two plugins are not made to be enabled in the same project.
2. Enable UTC Lens Tracing.
3. Open your levels. They load as they are: the Lite's cameras become the full version's, with their settings, and its four lenses are the same four of the kit.

From there the full tutorial applies as written.

Quick answers

Most surprises come from not looking through the lens tracing camera: check that first.

Problem	Fix
No lens effect	Look through the lens tracing camera, and check that Lens Data has a lens and Active Lens points to it (0 is the first slot).
Everything is soft	A new camera is focused at 1 km: use the eyedropper on your subject.
Black or dark corners	The sensor is larger than the lens's image circle: tick Recommended Sensor, or choose a smaller format.
The framing is tighter than expected	Unreal's default sensor is Super 35: pick 16:9 DSLR for full frame.
Shutter Speed or ISO doesn't change the brightness	Set Metering Mode to Manual. Still nothing: Exposure > Advanced > Exposure Method must be Enabled.
The lens tracing camera is a stop darker than Unreal's own	Its Exposure Compensation starts at 0, where Unreal's cameras add a stop.
The aperture won't open further	That is the lens's widest stop.
Grainy bokeh	Render grain: open the lens and raise Max Rays Per Pixel, or type r.LensTracer.SampleDensity 2 in the console. Both render slower.
My Movie Render Queue frames or my packaged game show no lens	The Lite traces in the editor only: see Where it renders.
I can't change a lens's surfaces	Lenses are read-only in the Lite: the Lens Editor is in the full version.
Glass, water or smoke is never in focus	The lens reads the depth of opaque surfaces only: tick Output Depth and Velocity in their material.
A soft halo around a sharp object in front of a very soft background	A known limit: stop down a little.
No lens flare	Reflections between the elements aren't traced, and Unreal's bloom, flares and vignette start off on the lens tracing camera. Turn them back on in its Post Process if you want them.
Nothing is traced at all	The lens needs DirectX 12 with Shader Model 6. Below it the camera renders as a plain Cine Camera and the Output Log warns once.

Requirements

Unreal Engine 5.8, Windows, DirectX 12 (Shader Model 6). TSR or TAA recommended. No project setting is needed; the plugin must be enabled when the editor launches.

Questions: contact@universaltoolcompiler.org